So it sounds like there are really 2 use cases here.

Use case 1: I give you an IP, can you find any useful information in that IP such as rack, datacenter, etc?

Use case 2: I'm less certain of this: I assign a big subnet to a smaller number of nodes and that subnet is essentially your "ring" size for something that shards. Allowing you to always send data for shard #1 to the same ip.

I'm definitely not a fan of the latter. I'd rather most app developers treat an IP as an opaque piece of data. 128 bits is alot of addresses but it's really not that much space for metadata.